Soil quality assessment in rice production systems Ana Cláudia Rodrigues de Lima Promotor: Prof. dr. L. Brussaard Hoogleraar Bodembiologie en biologische bodemkwaliteit Co-promotor: Dr. ir. W. B. Hoogmoed Universitair docent, leerstoelgroep Agrarische bedrijfstechnologie Promotiecommissie: Prof. dr. C. J. Ritsema (Wageningen Universiteit) Prof. dr. P. C. de Ruiter (Universiteit Utrecht) Prof. dr. ir. H. van Keulen (Wageningen Universiteit) Prof. dr. L. F. S. Pinto (Federal University of Pelotas, Brasil) Dit onderzoek is uitgevoerd binnen de onderzoekschool Production Ecology and Resource Conservation Soil quality assessment in rice production systems Ana Cláudia Rodrigues de Lima Proefschrift ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit Prof. Dr. M.J. Kropff in het openbaar te verdedigen op woensdag 7 november 2007 des namiddags te 16:00 uur in de Aula Lima, A.C.R. (2007). Soil quality assessment in rice production systems. PhD thesis, Wageningen University, The Netherlands. With summaries in English, Dutch and Portuguese. ISBN: 978-90-8504-761-2 Dedicated to: Farmers from “Banhado do Colégio”. Abstract In the state of Rio Grande do Sul, Brazil, rice production is one of the most important regional activities. Farmers are concerned that the land use practices for rice production in the Camaquã region may not be sustainable because of detrimental effects on soil quality. The study presented in this thesis aimed (a) to describe and understand how rice farmers assess soil quality; (b) to propose a minimum data set (MDS) to assess soil quality; (c) to establish which soil quality indicator(s) can be used to guide management leading to sustained crop production and (d) to reconcile local and scientific knowledge. To accomplish these objectives the research was based on two methodological procedures to assess soil quality: qualitative (local knowledge) and quantitative (scientific knowledge). The qualitative study led to the understanding of soil quality from a rice farmers’ perspective. Farmers from Camaquã were found to have detailed knowledge and a holistic view of the quality of the soil they are cultivating. Eleven indicators were mentioned as good soil quality indicators. Four out of these 11 soil quality indicators were considered “significant” by the farmers (soil colour, earthworms, soil organic matter and soil friability), while three indicators were found to be “useful” by the farmers in their decision-making: spontaneous vegetation, rice plant development and soil colour. In order to assess soil quality following a scientific approach, the three main management systems for irrigated rice in Rio Grande do Sul were chosen: conventional (dry seedbed preparation and sowing, high tillage intensity), semi-direct (dry seedbed preparation and sowing, low tillage intensity), and pre-germinated (seedbed preparation and sowing on inundated fields, high tillage intensity). Twenty-one rice fields covering these management systems and two different soil great groups were selected for investigation. In each field, five replicate plots were randomly laid out within an area of 3 ha for sampling. From each plot, 29 soil properties were analysed to establish a MDS using statistical tools in a novel way. The MDS consists of eight significant soil quality indicators: available water, bulk density, mean weight diameter, organic matter, Zn, Cu, Mn and earthworm number. In order to define the usefulness of this scientific approach, and to compare this with the local knowledge, a soil quality index (SQI) was determined. This study demonstrated that soil quality was best assessed when using the entire indicators set of 29 indicators. However, the MDS and farmers’ indicators sets performed almost equally well as the entire indicators set in showing the same trends in differences between management systems, soil textural classes and soil functions. The semi-direct management system resulted in the highest overall SQI, followed by the pre-germinated and conventional systems. A further study was undertaken to assess the effects of the different rice management systems on the physical and chemical soil quality. The results also indicate that the semi-direct management system is more sustainable, whereas the pre-germinated and conventional systems appear to contribute to soil degradation. Finally, a review of the state of knowledge on earthworm diversity in Rio Grande do Sul revealed 36 species and 20 genera, belonging to a total of 7 families in the state. Nine species were found in the rice fields of Camaquã (all new records for the region), two species were reported for the first time for the Rio Grande do Sul state and a new native genus and species of Criodrilidae ( Guarani camaqua ) was described. It is concluded that statistical procedures identified soil quality indicators which can be applied to monitor soil quality of rice fields and to support management decisions. Using an integrated approach may therefore increase the understanding of the complex nature of soil. Contents CHAPTER 1..............................................................................................................................1 General Introduction. CHAPTER 2..............................................................................................................................9 Farmer’s assessment of soil quality in rice production systems. A.C.R. Lima, W.B. Hoogmoed and L. Brussaard. CHAPTER 3............................................................................................................................25 Soil quality assessment in rice production systems: establishing a minimum data set. A.C.R. Lima, W.B. Hoogmoed and L. Brussaard. CHAPTER 4............................................................................................................................41 Functional evaluation of three soil quality indicator sets of three rice management systems. A.C.R. Lima, M.R. Tótola, R.G.M. de Goede, W.B. Hoogmoed and L. Brussaard. CHAPTER 5............................................................................................................................55 Management systems in irrigated rice affect physical and chemical soil properties. A.C.R. Lima, W.B. Hoogmoed and E.A. Pauletto. CHAPTER 6............................................................................................................................65 Earthworm diversity from Rio Grande do Sul, Brazil, with a new native Criodrilid genus and species (Oligochaeta: Criodrilidae). A.C.R. Lima and C. Rodríguez. CHAPTER 7............................................................................................................................79 General discussion and concluding remarks REFERENCES .......................................................................................................................87 SUMMARY.............................................................................................................................99 SAMENVATTING...............................................................................................................103 RESUMO...............................................................................................................................107 ACKNOWLEGEMENTS....................................................................................................111 ABOUT THE AUTHOR......................................................................................................113 PE&RC EDUCATION STATEMENT FORM .................................................................115 Chapter 1 General introduction 1.1. Soil quality Many definitions of soil quality have been proposed (Doran and Parkin, 1994; Larson and Pierce, 1994). Common to all the definitions is the capacity of soils to function effectively at present and in the future. An expanded version of this definition presents soil quality as: “the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation” (Karlen et al., 1997). However, no soil is likely to provide all these functions, some of which occur in natural ecosystems and some of which are the result of human modification (Govaerts et al., 2006). Soils have an inherent quality as related to their physical, chemical and biological properties within the constraints set by climate and ecosystems, but the ultimate determinant of soil quality is the land manager (Doran, 2002). Perceptions of what constitutes a good soil vary depending on individual priorities with respect to soil function, intended land use and interest of the observer (Doran and Parkin, 1994, Shukla et al., 2006). Within the framework of agricultural production, high soil quality equates to maintenance of high productivity without significant soil or environmental degradation (Govaerts et al., 2006). The assessment of soil quality can be viewed as a primary indicator of the sustainability of land management (Doran, 2002). Basically, two types of approach are employed for evaluating the sustainability of a management system: (i) comparative assessment and (ii) dynamic assessment. A comparative assessment is one in which the performance of the management system is evaluated in relation to alternatives at a given time only. In contrast, in a dynamic approach, the management system is evaluated in terms of its performance